Özet:

The paper analyzes laminar forced convection heat transfer for both single and mixture phase models utilizing Al2O3-water and CuO-water nanofluids as the working fluid and examines the effect of internal fins in the collector tubes in order to improve collector efficiency. A physical model with governing equations has been defined. Finite volume method has been utilized for discretizing governing equations and finite element method has been utilized for three-dimensional analysis of solar plate model with finned tubes. Convective heat transfer coefficient, Nusselt number and shear stress have been analyzed for Reynolds numbers from 200 to 700 with 0-5% volume fractions of nanofluid. Moreover, the efficiency of the collector has been investigated for constant flow rates from 0.02 to 0.04 mL/s and variable overall heat loss coefficient for the same range of volume fractions of nanofluid. It has been found that increment of shear stress and heat transfer coefficient occurred with the increment of concentration of nanoparticles and the Reynolds number. Investigation of particle size has not shown any notable variation with the mixture phase model. Mixture-phase model gives comparatively lower values due to the reduction of viscosity near the wall. Noticeable increment of efficiency has been observed by changing working fluid from Al2O3-water to CuO-water which has been further improved by utilizing variable overall heat loss coefficient. Efficiency increases up to 6.5% and 8.7% than the base fluid for utilizing Al2O3-water and CuO-water nanofluid respectively. Additionally, utilizing internal fins to the riser tubes, the efficiency increases up to 11%.

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